(AFP) - The European Parliament scrambled Monday to get ahead of the widening scandal of alleged huge cash bribes from figures working on behalf of World Cup host Qatar.

One of the assembly's vice presidents, Greek socialist Eva Kaili, has been charged with corruption by Belgian prosecutors and her assets have been frozen by her homeland.

Three of Kaili's associates have also been charged, after bags of cash were found in her home shortly after she returned from an official visit to Qatar, and a second MEP's house has been searched.

EU foreign ministers, arriving in Brussels to discuss sanctions against Iran and Russia, warned that the scandal threatens the credibility of European institutions.

"The allegations against the vice president of the European Parliament are of utmost concern, very serious," European Commission President Ursula von der Leyen said.

"It is a question of confidence of people into our institutions, and this confidence and trust into our institutions needs higher standards."

In Strasbourg, the president of the parliament, Maltese conservative Roberta Metsola -- who this weekend attended a police search of a Belgian MEP's home -- prepared to address the crisis.

According to parliamentary sources she would meet the leaders of the assembly's rival political groupings and address the issue from the podium at the opening of the week's session.

Kaili has been remanded in custody by an investigating magistrate in Belgium and has not travelled down to Strasbourg, the parliament's official seat, for the plenary session.

She received a new legal blow on Monday, when Greek authorities froze the 44-year-old former television presenter and her relatives' assets.

Several MEPs as well as transparency campaigners have called for tougher anti-graft rules.

- 'Insult to democracy' -

Manon Aubry, head of the Left group, called for Kaili's resignation and a commission of inquiry into what she called the parliament's "failures" in the affair.

"This will be a good week to fight corruption!" tweeted German Green MEP Daniel Freund.

Parliament's agenda this week will be overshadowed by the scandal, and Wednesday's debate on "the defence of democracies against foreign interference" now looks timely.

French socialist Aurore Lalucq wrote: "If the evidence is proven, this case is an insult. An insult to citizens, an insult to Europeans. An insult to democracy. An insult to Europe."

Qatar had been hoping that its diplomatic outreach, and the glow of hosting of the World Cup, would secure EU visa liberalisation for its citizens.

Doha "categorically" denied involvement in any wrongdoing.

The European Parliament often votes to criticise corruption abroad and has pushed for action against member states accused of breaking Brussels' rules, like Viktor Orban's Hungary.

But EU member state ministers meeting in Brussels, like Irish Foreign Minister Simon Coveney, warned that the scandal was "damaging".

"This is really an unbelievable incident that must now be cleared up, without ifs and buts, with the full force of the law," German Foreign Minister Annalena Baerbock said.

"Because this is also and especially about Europe's credibility and consequences must follow."

Belgian prosecutors revealed on Sunday that four suspects had been charged "with participation in a criminal organisation, money laundering and corruption".

The arrests followed raids in Brussels which prosecutors said turned up 600,000 euros ($630,000) in cash. Police also seized computers and mobile phones.

- Caught red-handed -

A judicial source confirmed to AFP that Kaili was one of the four charged, after large sums of cash were found in her home doing a police search.

Separately, police searched the home of Belgian socialist MEP Marc Tarabella, vice-chair of the parliamentary delegation "for relations with the Arab peninsula".

He has not been charged. Metsola's office said she had returned early from Malta to attend the search, as required by Belgium's constitution.

Kaili has been stripped of her responsibilities as a vice president of the parliament, notably that of representing Metsola in the Middle East.

But she remains an MEP and would normally enjoy immunity from criminal prosecution, except in cases where a suspect is caught red-handed in the act of committing an alleged crime.

Kaili visited Qatar just ahead of the World Cup and praised the country as a "frontrunner in labour rights", a sentiment she has repeated on the floor of the parliament.

© Agence France-Presse